Traction devices and traction systems for elevator arrangements are known to those skilled in the art. Ropes or belts are frequently used, with flat belts, V-ribbed belts or toothed belts being used as belts.
Where ropes are used as a traction device, each individual rope is clearly assigned a dedicated rope groove on the traction sheave or other sheave that drives the traction device. In this arrangement, each rope penetrates with at least part of the diameter thereof into the associated rope groove. Each individual rope is an independent tension element and can also be operated individually. For higher power requirements, it is possible to use either a plurality of ropes in parallel or the rope diameter can be increased. The individual rope is not only a traction device for transmitting the pulling forces but also participates directly in the transmission of the traction forces. Ropes as a traction device have the advantage that the force can be transmitted directly from the traction sheave to the ropes.
Where belts are used as a traction device, a plurality of adjacent ropes as tension members are always embedded in a common elastomer belt body. Here, the tension members are completely jacketed and surrounded by the elastomer material of the belt body and embedded therein. The plane of the tension members is far above the contact surface formed by the belt with the corresponding belt sheave, it being possible to consider the belt toothing as the contact surface in the case of toothed belts, the plane of the V as the contact surface in the case of V ribs, and the flat belt surface itself as the contact surface in the case of flat belts. A rubber layer, which is thick in comparison with the diameter of the tension member, is arranged between the tension member and the corresponding belt sheave. Here, the tension members are exclusively responsible for transmitting the pulling forces, while the elastomer material transmits the traction forces. The belt as a traction device, especially the elastomer region between the tension members and the contact surface, is thus exposed to high shear and shearing stresses during operation, and there is therefore the risk of fatigue in the elastomer material.
EP 1 396 458 A2 discloses an elevator device, for example, in which a flat belt made of elastomer material reinforced with tension members is used as a traction device. U.S. Pat. No. 7,757,817 B2 discloses an elevator system having a V-ribbed belt.
Compared with individual ropes, belts offer the advantage, on the one hand, that handling is simpler since, when constructing or servicing the belt drive, it is not necessary to lay each individual rope onto each corresponding groove of the traction sheave but only the elastomer body in which the tension members are embedded. Moreover, small traction sheave diameters can be employed since the embedded tension members generally have relatively small diameters. Moreover, belts as a traction device are virtually maintenance-free since no lubrication is required. However, the force that can be transmitted is dependent not only on the friction between the traction sheave and the elastomer but also, inter alia, on the shear strength of the elastomer material. Owing to the shear on the elastomer material, a belt of this kind is prone to fatigue.
For safety reasons, at least two and, in general, three to five belts must always be used in parallel in elevator installations. Since the belts contain a large number of thin tension members (individual ropes), the belt is relatively wide in comparison with a rope of the same strength. If a plurality of belts is now used in parallel, relatively wide traction sheaves and direction-changing sheaves are required.
U.S. Pat. No. 6,739,433 discloses a traction device for an elevator installation which is embodied as a profiled flat belt, thus increasing the size of the surface available for friction between the traction sheave and the belt. The force that can be transmitted is thus greater than in the case of an unprofiled flat belt but, here too, the zone of force transmission between the traction sheave and the traction device is still a significant distance from the tension members, owing to the elastomer layer of the elastomer body, which is thick in comparison with the diameter of a tension member, with the result that the elastomer material of the flat belt is likewise subjected to severe shear stress.
U.S. patent application publication 2010/0044158 A1 discloses a traction device which includes a plurality of tension members in the form of steel ropes arranged adjacent to each other and at a distance from each other, which are jacketed with elastomer and are connected by a common back layer.